170 THE GEOLOGICAL SUCCESSION 



eate the mode of life of the animal to which it belonged, 

 and to show that it fed on vegetables, {is the other organs 

 of the body constantly correspond in structural adaptation 

 to the same function. There is the utmost harmony and 

 adaptation of parts to each other amongst the several bones 

 of the skeleton, and hence each, taken by itself, indicates 

 and gives form to all the others. This has been shown by 

 the acute and laborious researches of Cuvier and Owea. 



There is every reason to believe that the history of the 

 development of vegetation on any barren rock, or newly 

 formed coral island, illustrates those stages by which the 

 earth itself became covered Vith verdure. The first vege- 

 table denizens of the rocky surface in modern times, are 

 usually cryptogamous plants, such as crustaceous lichens, 

 these are succeeded by the foliaceous species, and by such 

 mosses as Polytrichum commune, Hedwigia ciliata, and the 

 diflFerent varieties of Leskia and Hypnum, plants which are 

 of very humble growth, and of exceedingly simple structure, 

 consisting, comparatively speaking, of only a few cells. 

 The oxalic acid contained in the thalli of the lichens, to- 

 gether with the oxygen of the atmosphere, slowly disin- 

 tegrate tlie rocky surface, and successive generations of 

 these lowly protophy tes finally create a humus which gives 

 birth to a more highly organized vegetation. The higher 

 cryptogamia now make their appearance, Polypodium vul- 

 gare, Asplenium trichomanes, Asplenium ebeneum, together 

 with the Saxifrages, Arenarias, Aquilegia Canadensis and 

 other phanerogamous plants. Such appears to be the order 

 of nature — ^the cellular Cryptogamia preparing the way for 

 ferns and flowering plants — ^the simple preceding the com- 

 plex. 



That cryptogamous plants are the most ancient inhabi- 

 tants of the earth ; that they existed anterior to the Pha- 



